HIV-1 prevalence and risk factors among sexually transmitted disease clinic attenders in Trinidad

OBJECTIVES

To study trends in prevalence and to ascertain risk factors for HIV-1 among sexually transmitted disease (STD) clinic attenders in Trinidad.

DESIGN AND METHODS

Serial cross-sectional studies were conducted in 1987-1988 and 1990-1991 at a centralized STD clinic in Port of Spain. A case-control study was carried out to examine in greater detail the demographic and behavioral risk factors for HIV-1 among self-declared heterosexuals in this population.

RESULTS

HIV-1 prevalence increased from 3.0% [95% confidence interval (CI), 2.3-3.9] in 1987-1988 to 13.6% (95% CI, 11.8-15.6) in 1990-1991. Age > or = 40 years [odds ratio (OR), 2.0; 95% CI, 1.4-2.8], urban residence (OR, 2.2; 95% CI, 1.6-3.0), and human T-lymphotropic virus-I seropositivity (OR, 3.1; 95% CI, 1.6-6.0) were significant risk factors for HIV-1 in 1990-1991. In the case-control analysis, significant independent risk factors for men included current genital ulcer disease (OR, 5.2; 95% CI, 2.2-12.5), current genital warts (OR, 3.9; 95% CI, 1.2-12.0), having ever had syphilis (OR, 3.2; 95% CI 1.6-6.1), and use of crack cocaine in the preceding 6 months (OR, 6.2; 95% CI, 2.7-14.2). Corresponding risk factors for women were commercial sex work (OR, 5.7; 95% CI, 1.3-25.7), initiation of sexual activity before age 14 years (OR, 4.8; 95% CI, 1.5-16.0), and past non-gonococcal cervicitis (OR, 4.1; 95% CI, 1.3-13.1).

CONCLUSIONS

HIV-1 in this setting is primarily heterosexually transmitted in a milieu of unprotected sexual activity fuelled by a crack cocaine epidemic. Targeted interventions to prevent, detect and treat STD and crack cocaine addiction, as well as disrupt their adverse synergism, may substantially reduce HIV-1 transmission in this population.

Variation in cancer risk estimates for exposure to powerline frequency electromagnetic fields: a meta-analysis comparing EMF measurement methods

We used meta-analysis to synthesize the findings from eleven case-control studies on cancer risks in humans exposed to 50-60 Hertz powerline electromagnetic fields (EMFs). Pooled estimates of risk are derived for different EMF measurement methods and types of cancer. EMF measurement methods are classified as: wiring configuration codes, distance to power distribution equipment, spot measurements of magnetic fields, and calculated indices based on distance to power distribution equipment and historic load data. Pooled odds ratios depicting the risk of cancer by each measurement type are presented for all cancers combined, leukemia for all age groups and childhood leukemia. The wire code measurement technique was associated with a significantly increased risk for all three cancer types, while spot measures consistently showed non-significant odds ratios. Distance measures and the calculated indices produced risk estimates which were significant only for leukemia.

Educational and consultative functions, topics, and methods of hospital general tumor conferences

The educational and consultative functions, topics, and methods of 20 hospital general tumor conferences in Colorado were studied over a three-year period. Methods used included questionnaires completed by hospital admitting staff members, by tumor conference directors, and by conference attendees. Workshops were held in which a multidisciplinary panel of physicians, nurses, and cancer registrars discussed the educational and patient-management aspects of tumor conferences with tumor conference directors. The study design included evaluation of the effects of providing certain teaching aids, including newsletters, Physician Data Query printouts, and tumor registry data on the functions, topics, and methods of the conferences. Although certain temporal trends were suggested, the handouts as employed added little of perceived effectiveness for the busy clinicians attending. The characteristics of the tumor conferences were analyzed according to hospital size, presence of one or more residency programs, and location (metropolitan or otherwise). One observation was that relatively few primary care physicians attended these tumor conferences, especially those in large hospitals, and approaches to meeting the needs of that group are discussed. The importance of the interpersonal skills of the tumor conference director in the effectiveness of the conference was very evident.

Molecular cloning, DNA sequence analysis, and characterization of the Corynebacterium diphtheriae dtxR homolog from Brevibacterium lactofermentum

A homolog of the Corynebacterium diphtheriae dtxR gene was isolated from Brevibacterium lactofermentum. The product of the B. lactofermentum dtxR gene was immunoreactive with polyclonal anti-DtxR antibodies and functioned as an iron-activated repressor capable of regulating the expression of beta-galactosidase from a diphtheria tox promoter/operator transcriptional fusion in recombinant Escherichia coli. The extents of induction by increasing concentrations of the chelator 2,2'-dipyridyl were identical in cells expressing DtxR from either C. diphtheriae or B. lactofermentum.

Campylobacter diarrhea in Alexandria, Egypt

The role of Campylobacter as a cause of bacterial diarrhea in young children in Alexandria, Egypt was investigated. Stools or rectal swabs were collected from 880 children (mean age 9.8 months) presenting to a hospital with the primary complaint of diarrhea and from 1,079 well children (mean age 8.8 months) attending a vaccination clinic. Isolation of Campylobacter was significantly (p<0.0002) more frequent from cases (17.2%) than from controls (6.4%). Campylobacter was isolated from children presenting with diarrhea more frequently than Salmonella (3% isolation rate), Shigella (2% isolation rate), or other bacterial pathogens (1% isolatoin rate). Isolation of Campylobacter was significantly more frequent during the rainy season (p<0.0012). These results implicate Campylobacter as a major bacterial cause of diarrhea for which young children are brought for medical attention in Alexandria, Egypt.

Effect of supplementation with an iron-fortified milk on incidence of diarrhea and respiratory infection in urban-resident infants

To address the hypothesis that increased infectious morbidity is associated with iron supplementation, 783 randomly selected infants were provided with a powdered full fat cow's milk (non-fortified group) and 872 with a powdered acidified full fat cow's milk fortified with 15 mg of iron as ferrous sulfate (fortified group). All infants were followed from birth to 15 months of age with a monthly home visit by a nurse who recorded morbidity occurring during the previous 30 days. At 9 months of age, 15% of infants in each cohort were receiving breast milk only; data for these infants were segregated to make the third group. Episodes (mean +/- SD) of diarrhea/infant/year were 1.06 +/- 1.29, 1.14 +/- 1.37, and 0.82 +/- 1.04 for the fortified, non-fortified and breast-fed groups, respectively; the fortified and non-fortified bottle-fed groups had a very similar incidence of respiratory illness; 2.66 +/- 2.07 and 2.74 +/- 2.24 episodes/infant/year, respectively. The incidence of respiratory illness for both bottle-fed groups was significantly higher than that for the breast-fed group (2.22 +/- 1.84 respiratory episodes/infant/year). We conclude that for the infants the tested form of iron fortified milk, which is sufficient to lower iron deficiency anemia, does not result in an increased incidence of diarrhea or respiratory illness.

Crystallization and preliminary X-ray studies of the diphtheria Tox repressor from Corynebacterium diphtheriae

Crystals of the diphtheria tox repressor (DtxR) from Corynebacterium diphtheriae suitable for structure determination have been obtained. DtxR activated with transition metal ions represses the expression of the structural gene for the diphtheria toxin, tox, which is encoded on the genome of a family of closely related corynebacteriophages. The space group of the obtained crystals is trigonal P3(1)21 or its enantiomorph P3(2)21 with a = b = 64.2 A, c = 220.5 A, alpha = beta = 90 degrees, gamma = 120 degrees. Two monomers comprise the asymmetric unit. The crystals diffract to a resolution of better than 3 A.

Low doses of interferon-alpha are as effective as higher doses in inducing remissions and prolonging survival in chronic myeloid leukemia

OBJECTIVE

To determine the toxicity and efficacy of low-dose interferon-alpha therapy in inducing remissions and prolonging survival in patients with chronic myeloid leukemia.

DESIGN

Phase II evaluation and comparison with historical control patients and other series in which the investigators used higher interferon-alpha doses.

SETTING

Tertiary care leukemia research clinic.

PATIENTS

41 patients with newly diagnosed or previously treated chronic-phase, Philadelphia chromosome-positive chronic myeloid leukemia received interferon-alpha at a dose of 2 x 10(6) U/m2 body surface area daily for 28 days and then three times weekly.

MEASUREMENTS

Complete blood counts and physical examinations were done monthly to determine hematologic remission and toxicity. To determine karyotypic response, bone marrow cytogenetic analyses were done at 6 monthly intervals in patients who achieved a complete hematologic remission. In addition, Kaplan-Meier survival curves and median survival values were generated from diagnosis and the start of therapy with interferon-alpha.

RESULTS

70% of patients treated with low-dose interferon-alpha within 1 year of diagnosis achieved a complete hematologic remission, and 22% of these patients had a major or complete karyotypic response. Investigators who used higher interferon-alpha doses in similar patient populations have reported complete hematologic remission rates of 59% to 70% and major and complete cytogenetic response rates of 16% to 29%. The Kaplan-Meier estimated 5-year survival rate of minimally pretreated patients in our study is 73% (95% CI, 51% to 95%), which compares favorably with survivals reported by investigators who used higher doses. The estimated yearly cost of the interferon-alpha used in our study is $5953 compared with a median of $24,375 for the higher doses used by other investigators. Less toxicity was also observed.

CONCLUSION

Low-dose interferon-alpha is as effective as higher-dose interferon-alpha in inducing remissions and prolonging survival in patients with chronic myeloid leukemia but is considerably less expensive and toxic.

Iron, DtxR, and the regulation of diphtheria toxin expression

In recent years considerable advances have been made in the understanding of the molecular basis of iron-mediated regulation of diphtheria toxin expression. The tox gene has been shown to be regulated by the heavy metal ion-activated regulatory element DtxR. In the presence of divalent heavy metal ions, DtxR becomes activated and binds to a 9 bp interrupted palindromic sequence. The consensus-binding site has been determined by both the sequence analysis of DtxR-responsive operators cloned from genomic libraries of Corynebacterium diphtheriae as well as by in vitro genetic methods using cyclic amplification of selected targets (CASTing). It is now clear that DtxR functions as a global iron-sensitive regulatory element in the control of gene expression in C. diphtheriae. In addition, the metal ion-activation domain of DtxR is being characterized by both mutational analysis and determination of the X-ray structure at 3.0 A resolution.

Determination of the minimal essential nucleotide sequence for diphtheria tox repressor binding by in vitro affinity selection

The expression of diphtheria toxin in lysogenic toxigenic strains of Corynebacterium diphtheriae is controlled by the heavy metal ion-activated regulatory protein DtxR. In the presence of divalent heavy metal ions, DtxR specifically binds to the diphtheria tox operator and protects a 27-bp interrupted palindromic sequence from DNase I digestion. To determine the consensus DNA sequence for DtxR binding, we have used gel electrophoresis mobility-shift assay and polymerase chain reaction (PCR) amplification for in vitro affinity selection of DNA binding sequences from a universe of 6.9 x 10(10) variants. After 10 rounds of in vitro affinity selection, each round coupled with 30 cycles of PCR amplification, we isolated and characterized a family of DNA sequences that function as DtxR-responsive genetic elements both in vitro and in vivo. Moreover, these DNA sequences were found to bind activated DtxR with an affinity similar to that of the wild-type tox operator. The DNA sequence analysis of 21 unique in vitro affinity-selected binding sites has revealed the minimal essential nucleotide sequence for DtxR binding to be a 9-bp palindrome separated by a single base pair.

Diphtheria toxin-related cytokine fusion proteins: elongation factor 2 as a target for the treatment of neoplastic disease

We have used protein engineering and recombinant DNA methodologies in order to construct a fusion protein in which human interleukin-2 (IL-2) is genetically linked to the catalytic and transmembrane domains of diphtheria toxin. The fusion toxin, DAB486IL-2, is highly cytotoxic for only those cells which display the high affinity interleukin-2 receptor (IL-2R) on their surface. In phase I/II clinical studies the intravenous administration of DAB486IL-2 has been found to be safe, well tolerated and may lead to the induction of durable remissions in patients presenting with a variety of IL-2R positive lymphomas.

An intact transmembrane helix 9 is essential for the efficient delivery of the diphtheria toxin catalytic domain to the cytosol of target cells

To investigate structure/function relationships involved in the delivery of the diphtheria toxin (DT) catalytic (C) domain to the cytosol of target cells, we have constructed and characterized internal in-frame deletion mutants in the transmembrane (T) domain of the fusion toxin DAB389IL-2. This fusion protein is composed of the C and T domains of DT to which human interleukin-2 (IL-2) has been genetically fused. The mutant fusion toxins were compared to DAB389IL-2 with respect to cytotoxic potency, receptor binding affinity, channel formation in planar lipid membranes, and sensitivity to proteolytic digestion. We demonstrate that genetic fusion of human IL-2 sequences to a diphtheria toxin-related fragment that contains less than full-length transmembrane helix 9 results in a fusion protein that binds to the high affinity IL-2 receptor, but has lost > or = 3 logs of cytotoxic potency and has decreased ability to insert into planar membranes and form stable channels. These observations are consistent with the hypothesis that an intact transmembrane helix 9 is essential for the formation of stable channels that are required for the efficient delivery of the C domain to the cytosol of target cells.

Maintenance of the hydrophobic face of the diphtheria toxin amphipathic transmembrane helix 1 is essential for the efficient delivery of the catalytic domain to the cytosol of target cells

The transmembrane (T) domain of diphtheria toxin (DT) comprises nine alpha-helices and has been shown to play an essential role in the efficient delivery of the catalytic (C) domain of DT across the eukaryotic cell membrane and into the cytosol. We have demonstrated recently that the first three amphipathic helixes of the T domain, although not necessary for either channel formation or receptor binding, are required for the efficient transmembrane delivery of the C domain. In the present study, we have performed a detailed structure-function analysis of T domain helix 1 (TH1) of the DT-related fusion protein DAB389IL-2. We performed exchange and site-directed mutagenesis of TH1 and the resulting mutant fusion toxins were analyzed by gel electrophoresis and tested for their efficiencies in the delivery of the C domain to the cell cytosol. We demonstrate that the overall charge distribution and hydrophobicity of amino acids in the amphipathic helix TH1, rather than a specific amino acid sequence, are critical for the function of this helix. The insertion of a charged residue in the hydrophobic face of TH1 abolishes cytotoxic activity, whereas replacement of a hydrophobic residue by a charged amino acid in the hydrophilic face of the helix has little, if any, effect on cytotoxic activity. In addition, we have identified Ser220 by site-directed mutagenesis as a residue that appears to be critical for correct folding of the fusion toxin. Mutations in this position result in fusion proteins that are extremely sensitive to proteolytic attack.

Inhibition of AIDS-associated Kaposi's sarcoma cell growth by DAB389-interleukin 6

Acquired immune deficiency syndrome-associated Kaposi's sarcoma (AIDS-KS)-derived spindle cells produce and use interleukin 6 (IL-6) among several other cytokines as a growth factor. In this study we show that AIDS-KS cells express approximately 1100 high-affinity IL-6 receptors (IL-6R) per cell with a dissociation constant (Kd) of 110 pM. Furthermore, AIDS-KS cells express the IL-6R alpha subunit, detected as a single 5.0-kb messenger ribonucleic acid species, and the high-affinity converting, signal-transducing IL-6R beta subunit designated as gp130. Similarly, tumor tissue obtained from patients with KS and AIDS expresses IL-6R messenger ribonucleic acid. We have exploited the chimeric fusion toxin DAB389-IL-6, which exerts cellular toxicity only to the cells expressing IL-6R. This chimeric protein was engineered by fusion of a truncated diphtheria toxin structural gene, in which the region encoding the native receptor-binding domain was removed and replaced with the gene encoding IL-6. DAB389-IL-6 inhibited protein synthesis in AIDS-KS-derived spindle cells at very low concentrations (IC50 of 3.4 x 10(-11) M). Similarly, inhibition of cell viability by DAB389-IL-6 was observed at equivalent dose levels (IC50 of 5 x 10(-11)). These effects on protein synthesis and cell viability can be abrogated by recombinant human IL-6, indicating receptor specificity. Thus, DAB389-IL-6 is a potential agent for the treatment of AIDS-associated KS.

Treatment of ALS with high dose pulse cyclophosphamide

Autoimmune abnormalities have been described in sporadically acquired amyotrophic lateral sclerosis (ALS), but ALS patients do not benefit from conventional immunosuppressive therapy. Because Multifocal Motor Neuropathy causes a syndrome mimicking the lower motor neuron involvement in ALS and responds to high dose cyclophosphamide, we tested whether ALS patients would respond to the same treatment. Eighteen patients with classical ALS initially received a high loading dose of intravenous cyclophosphamide (3 g/m2) followed by 6-monthly injections of 750-1000 mg/m2. We monitored isometric strength, fine motor coordination and pulmonary function monthly for 3 months prior to the study, during the treatment phase, and for 6 months after treatment. Treatment subjects were matched to control subjects from the WALS natural history data base and compared on the basis of decline rate (megaslopes). Treatment did not alter the course of ALS.

Epitope tagging of DAB389IL-2: new insights into C-domain delivery to the cytosol of target cells

The fusion toxin DAB389IL-2 is composed of the catalytic (C) and transmembrane (T) domains of native diphtheria toxin to which human interleukin-2 (IL-2) has been genetically fused (1,2). Following binding to the IL-2 receptor, the fusion toxin is internalized by receptor mediated endocytosis, and upon acidification of the endocytic vesicle, the T domain spontaneously inserts into the membrane, and facilitates the delivery of the C domain to the cytosol (3,4). In order to further study the process by which the C domain is delivered to the target cell cytosol, we genetically fused an eleven amino acid epitope derived from the vesicular stomatitis virus (VSV) G protein to the N-terminal end of DAB389IL-2. The epitope labelled fusion toxin, VSV-G-DAB389IL-2, was found to retain IL-2 receptor specific binding and cytotoxic activity. Target cells were incubated for various times in the presence of VSV-G-DAB389, fixed and then treated with anti-VSV G and FITC conjugated secondary antibody. Laser scanning confocal microscopy was used to determine the location of the fluorescent signal. The VSV-G epitope tagged fusion toxin was found only to be associated with small vesicles that were situated adjacent to the plasma membrane. These results suggest that the C domain of the fusion toxin is associated with an early intracellular compartment and is rapidly delivered to the cytosol. Since channel formation by the T domain is necessary for the delivery of the C domain, it follows that T domain insertion into the membrane also occurs early in the intoxication pathway.

Sample size determination for an exponential survival model with an unrestricted covariate

We derive formulae for estimating sample size and power for detecting the effect of an unrestricted covariate on survival time. These are useful in designing survival studies with different patterns of recruitment and follow-up when survival time is exponentially distributed. We use the asymptotic covariance matrix, conditional expectation and Taylor's expansion techniques to develop these formulae. Computer simulations indicate that the asymptotic approximations used in developing the formulae are good over a range of parameter values and different patterns of recruitment and follow-up that are relevant to survival studies.

A structured literature review for risk assessment: EMF and human health risk

The volume of publications on any given topic makes it difficult to select an appropriate subset of publications for review by an expert panel. This paper proposes a method for selecting a subset using a protocol that attempts to order publications based upon good research methods. The protocol was followed by graduate students with no expert knowledge of the area they were reviewing. They reduced 11730 articles on the topic of EMF and Health risk to 68 articles that were reviewed by an expert panel. The interrater reliability was 96% and 94% of the relevant articles were captured by this process.

Diarrhoeal disease: current concepts and future challenges. Rapid detection of enteric infections by measurement of enteric pathogen-specific antibody secreting cells in peripheral blood

Enteric infections and diarrhoeal disease are important causes of morbidity and mortality. Infections are often difficult to diagnose, especially when access to sophisticated laboratory facilities is limited. In an attempt to develop a rapid method of diagnosis, which might not require an advanced laboratory, advantage was taken of the observation that precursors of lymphocytes secreting immunoglobulin A (IgA), generated in response to mucosal stimulation with an antigen, are transiently present in peripheral blood. Detection of cells in peripheral blood bearing IgA specific for a pathogenic microbe should indicate current infection. This hypothesis was tested using peripheral blood mononuclear cells collected from volunteers who were clinically 'normal', had experimentally induced shigellosis, had naturally acquired shigellosis, or had naturally acquired typhoid fever. The method was sensitive for detection of Salmonella typhi infection and less sensitive for detection of Shigella infection. The antibody secreting cell procedure has good potential as a rapid, simple diagnostic procedure if applied during the acute phase of infection.

Activation and enhanced contact of human T-lymphocytes with autologous red blood cells are required for their stable adherence at 37 degrees

The adherence of human red blood cells (RBC) to autologous T-cells does not occur in the body, and in vitro is elicited at 4 degrees. Autologous E-rosetting at 37 degrees has not previously been described. In this work, lymphocyte-RBC adherence has been studied in mixed leukocyte-RBC cultures and in whole blood from healthy donors. Vital, cytochemical and electron microscopic studies have shown that T-cells may form stable E-rosettes with autologous RBC at 37 degrees. As in the previously reported cold-dependent reversible rosetting, stable rosetting is mediated by the erythrocyte LFA3 and lymphocyte CD2 molecules. Uniquely, this phenomenon requires both T-cell activation and an enhanced contact between the T-cell and RBC membranes. These requirements were met by exposure of cell cultures to: (1) PHAE, the erythroagglutinating component of PHAP, or (2) to either non-erythroagglutinating mitogens, PHAL, Con A, OKT3 or SEA, or to antigens of typhus group rickettsiae or salmonellae, provided that the RBC membrane was desialyted. Cultures derived from individuals seropositive to rickettsiae or vaccinated with salmonellae demonstrated the adherence phenomenon after antigen exposure when neuraminidase was present in the culture medium. The system 2 described here can be used as a diagnostic tool for defining activated T-cells and T-cell clones with the memory to antigens capable of inducing cell-mediated immunity.

Evaluation of an intervention to change benzodiazepine-prescribing behavior in a prepaid group practice setting

To determine the effect of two levels of educational intervention on benzodiazepine-prescribing behavior in an elderly population in a controlled prepaid group practice (PPGP) setting, we designed a prospective controlled trial, with six-month follow-up. Our setting was a 270,000 member group-model PPGP in Colorado, from 1990 to 1991. Participants included 91 physicians, 62 men and 29 women; median age was 38.7 years. Group 1 received a one-on-one educational presentation by a clinical pharmacist, written educational materials, a brief follow-up visit, and feedback with recommendations. Group 2 received only a face-to-face presentation, given to departmental groups, as well as the same written educational materials used in group 1. Controls received no intervention. Our primary outcome measure was the benzodiazepine "on/off" status of the elderly PPGP members. The secondary outcome measure was the median change (preintervention minus postintervention) in a standardized amount of benzodiazepines prescribed per physician. Logistic regression analysis failed to show a significant effect on postintervention benzodiazepine on/off status between study groups, when controlling for preintervention on/off status, PPGP-member age, PPGP-member gender, and all possible interactions. Analysis of variance failed to demonstrate an effect of either intervention on the median change in standardized amount of benzodiazepines prescribed per physician, with groups 1, 2, and controls yielding values of -278 (range: -4,137, 2,844), -330 (-1,531, 1,358), and -541 (range: -3,716, 2,185), respectively. We conclude that strategies effective in changing physician prescribing behavior in other settings may not be effective in a PPGP setting with benzodiazepines in the elderly as the target for change.

Cytotoxicity of a recombinant diphtheria toxin-granulocyte colony-stimulating factor fusion protein on human leukemic blast cells

Granulocyte colony-stimulating factor (G-CSF) is a potent stimulator of the growth of normal and malignant hematopoietic cells and synergizes with other factors such as interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The action of G-CSF is mediated through a specific membrane receptor, however it is not clear if all of the effects of G-CSF are direct or indirect. As a step towards addressing this problem, a recombinant diphtheria toxin (DT)-related human G-CSF fusion protein has been constructed and purified from E. coli. The 70,000 dalton chimeric protein has immunologic determinants characteristic of both DT and G-CSF. At high concentrations, DAB486-G-CSF is cytotoxic towards G-CSF-dependent OCI/AML1 cells, but not factor independent OCI/AML3 cells; colony formation by G-CSF-responsive leukemic blasts from a patient with acute myeloblastic leukemia (AML) was also inhibited. The G-CSF fusion toxin displayed ADP-ribosyltransferase activity in a cell-free system. Genetic conjugation of G-CSF to an enzymatically inactive DT mutant, CRM197, resulted in a 200-fold reduction in the ability of G-CSF to stimulate normal bone marrow colony formation. These results suggest that fusion of G-CSF to DT sequences interferes with some of the activity but not the specificity of the ligand binding domain of the molecule. Nevertheless, DAB486-G-CSF may be included with the increasing number of other toxin-hormone fusion proteins whose toxicity is directed towards specific receptor-bearing cells, and may represent a novel approach towards the study and treatment of leukemia.